The present invention relates to pumps and, in particular, to pumps having accurate pumping rates and pumping volumes.
Fluid pumps are typically based upon the use of a rotating or reciprocating device such as an impeller which is bearing mounted and driven by some motive means such as an electric motor. Such mechanical pumps, while reasonably efficient, uniformly suffer from the problems of wear of the moving parts as well as significant levels of audible noise. In order to solve the problems of wear, a pump having essentially no moving parts was developed and is disclosed in my U.S. Pat. No. 3,898,017, issued Aug. 5, 1975. In that patent, the heater ribbon is placed in the chamber containing the pumped fluid. This allows the fluid being pumped to come in contact with the heating ribbon. Such direct contact may not be desirable in some medical applications where it is desired to pump fluids having a delicate or fragile structure or which are subject to breakdown in the presence of high temperature. In addition, it is frequently necessary to keep the pumped fluid separated from a reusable heater to maintain a sterile environment for the pumped fluid. Such was not possible in the prior patent.
The present invention in meeting these problems provides a pump which incorporates a movable diaphragm for separating the fluid being pumped from the heating ribbon or element so that the pumped fluid is not affected by the heat from the heating element, and further will not be contaminated by contaminants which may exist around the heating element or in the chamber in which the heating element is placed. The pumping of the pumped fluid thus occurs in response to the expansion and contraction of a pumping fluid which is different from the pumped fluid and which preferably has a high expansion ratio and low specific heat. Although such a pumping fluid is preferably a gas, it may be a liquid or may be a fluid which changes state, for example, from a liquid to a gas upon heating and then back to a liquid when the heater is cool. In addition, the present invention in using a diaphragm in a pumping chamber with a fixed volume provides a means of very accurately defining the pumped volume of the fluid. This occurs by causing the diaphragm to be displaced by the pumping fluid upon its expansion against the sides of the pumping chamber thereby expelling all of the pumped fluid in the chamber. Thus, the volume of the fluid pumped on each cycle of the pump is accurately defined by the volume of the pumping chamber. The present invention also provides a means for easily adjusting the flow rate, as well as providing increased fluid pressures. The pump of the present invention may be a positive displacement type pump or may incorporate a variable displacement feature by controlling the amount by which the pumping fluid expands due to heating by the heater. Finally, the present pump invention is free of audible noise.
In U.S. Pat. No. 2,884,866 issued May 5, 1959, a pumping mechanism is disclosed which attempted to provide accurate pumping volumes. However, in that patent, no fixed volume chamber was provided to define an accurate per cycle pumped volume. Finally, the interior of the sock-type flexible member defining the cycle pumping volume could not be accurately evacuated on each cycle thus resulting in additional inaccuracy in pumping volume and rate. It will be appreciated that in many I.V. pumping applications, pumping accuracy unachievable by the above-cited patent but easily obtained by the present invention, is a necessity.
Various other apparatus using pistons (which have undesirable friction and sealing characteristics), manual or independent valve operation, single-cycle rather than continuous multiple-cycle operation, inter-mingling of the pumped and the pumping fluid, no volume-defining pumping chamber, and various other disadvantages are described in various of the U.S. Pat. Nos. 2,389,067; 2,576,282; 2,867,224; 2,884,866; 3,045,874; 3,074,596; 3,099,222; 3,149,754; 3,604,821; 3,645,649; 3,859,012; 3,901,629; and Re. 27,740.